Security systems are commonly available to monitor psychiatric patients, assist in confinement of prisoners, and track or discourage unauthorized use of aircraft, boats, cars, trucks, construction equipment, and other mobile high-value items (generally herein, xe2x80x9cvehiclesxe2x80x9d). Relatively elaborate and costly security systems (including vehicle recovery systems) may allow locating and/or tracking such vehicles using satellite navigation systems linked to a terrestrial network and/or through use of a directional antenna to receive omnidirectional transmissions from the tracked vehicle. Still other systems merely provide for disabling a vehicle and/or activation of a local alarm carried by the vehicle (using, e.g., flashing lights, horn or siren). These security systems vary widely in cost and capability. They generally operate independently or as part of a network requiring the payment of fees.
Sophisticated tracking and/or interception systems allow remote determination of vehicle direction which is useful for tracking a vehicle. Examples of such systems are described in U.S. Pat. No. 6,326,903 B1, incorporated herein by reference. Direction references described in the ""903 patent include those provided by magnetic compass and by using successive locations determined through GPS satellites. But GPS-based systems are relatively costly and complex, as noted above, and magnetic compasses are subject to significant potential errors due to magnetic declination as well as variable magnetic deviations resulting from magnetic materials and/or magnetic fields in the vicinity of the compass.
Other U.S. patents related to vehicle communications, security, tracking and/or monitoring include U.S. Pat. Nos. 4,818,998; 4,903,279; 4,908,629; 6,191,708; 6,292,724; 6,320,514; 6,320,535; 6,323,566; 6,326,903; 6,327,257; 6,329,901; 6,330,452; 6,331,825; 6,346,877; and 6,353,743, each incorporated herein by reference.
Taken together, the above examples and similar systems offer many useful features, but a single integrated system offering a comprehensive selection of features at a moderate price is not available. Such a system would provide timely, specific and effective security information locally and/or would communicate such information with one or more base stations spaced apart from the vehicle. Capabilities would include provisions for broad area coverage through a plurality of base stations, with coordinated monitoring of individual vehicle movement as well as control of traffic flow comprising one or more vehicles. Specific features underlying these capabilities would include, but not be limited to, means for estimating the location, heading, and speed of each vehicle, and its range from one or more base stations, in near real time.
The present invention comprises at least one addressable transponder for receiving security information addressed to it from at least one base station, and for transmitting security information to at least one base station. A transponder preferably automatically acknowledges receipt of security information from a base station via a transmission to one or more base stations. Each such acknowledgment transmission comprises at least one transponder address corresponding to the receiving transponder.
Each addressable transponder comprises an addressable transponder receiver, an addressable transponder transmitter connected to the transponder receiver, and a transponder antenna connected to the transponder receiver and the transponder transmitter. Each transponder receiver comprises a discriminator for rejecting base station transmissions not addressed to that transponder, together with a decoder to decode security information encoded in base station transmissions addressed to the transponder. Further, each transponder transmitter comprises an encoder for encoding security information comprising the transponder""s address in each transmission from that transponder.
And each transponder antenna comprises a steerable directional antenna and a steerable directional antenna azimuth sensor for providing security information comprising a transponder antenna azimuth indicative of each azimuth to which said steerable directional transponder antenna is steered.
The present invention also comprises at least one base station for receiving security information transmitted from at least one addressable transponder, for transmitting security information addressed to at least one such transponder, and for communicating security information with at least one operator.
Each base station comprises a base station transmitter, a base station receiver connected to the base station transmitter, a base station antenna connected to the base station transmitter and the base station receiver, and an operator interface connected to the base station transmitter and the base station receiver for bidirectional communication with at least one operator of security information (including security commands) received and/or transmitted by each base station.
Each base station receiver comprises a decoder to decode security information encoded in transmissions received from at least one addressable transponder. Further, each base station transmitter comprises an encoder for encoding security information comprising at least one transponder address in each transmission from that base station to at least one addressable transponder. And each base station antenna comprises a steerable directional antenna and a steerable directional antenna azimuth sensor for providing security information comprising a base station antenna azimuth indicative of each azimuth to which said steerable directional base station antenna is steered.
Transponder and base station antenna azimuths can provide valuable security information for locating and/or tracking a vehicle that carries the transponder. Thus, a transponder antenna is preferably mounted on a vehicle so that the transponder antenna azimuth is indicated by the antenna azimuth sensor relative to the vehicle (e.g., preferably relative to the direction of forward travel of the vehicle). A base station receiving a transmission of security information comprising such a transponder antenna azimuth can then estimate the heading of the vehicle in near real time.
Such vehicle heading estimates are made with respect to a (preferably previously established) base station antenna azimuth reference (for example, true north). By knowing both the azimuth of the base station antenna on which security information is received from the vehicle transponder, as well as the transponder antenna azimuth relative to the direction of forward travel of the vehicle, the heading of the vehicle with respect to the base station antenna azimuth reference (e.g., true north) may then be estimated as described herein below.
Heading information can reveal a vehicle""s orientation in traffic, and may also be used in conjunction with other security information described herein to predict a future location of the vehicle. These functional capabilities can in turn facilitate control of traffic flow and/or allow the vehicle""s interception and recovery. Note that since estimates of the vehicle heading in this example are made relative to the base station azimuth reference, the vehicle itself does not need an azimuth reference other than its own structure (as reflected, for example, in the vehicle""s direction of forward travel). In particular, the vehicle does not require access to an external reference such as might be provided by a magnetic compass or GPS receiver.
Thus, use of steerable directional antennas in both base stations and transponders of the present invention provides operational advantages not obtainable in other systems without directional antennas or in systems relying on use of directional antennas at only one end of a vehicle communication link. One such advantage relates to vehicle location. Several well-known techniques for vehicle location rely on triangulation, which may also be employed in the present invention for tracking and/or locating a vehicle carrying an addressable transponder. But alternative approaches are needed because triangulation requires at least two base station antenna azimuths (or analogous measures), and these azimuths may not always be available for locating a vehicle. And when only one azimuth is available, the present invention provides for an alternative technique for vehicle location.
This alternative technique involves estimation of the range from a base station is (or tracking vehicle) to a tracked vehicle with which the base station (or tracking vehicle) is communicating. The effective range of such communications is controllable in the present invention, preferably as a predetermined variable for each transmission from a base station and/or addressable transponder. Thus, in preferred embodiments of the present invention, effective transmission range is established by a transmission range controller in each transponder and/or base station transmitter as a function of transmission power and/or bandwidth.
Such effective transmission range control can be used, for example, to estimate the locations of addressable transponders around a base station. To make these estimates, the base station will typically transmit a relatively long-range signal on each of a plurality of base station antenna azimuths (for example, on successive azimuths at ten-degree increments around a full circle). Each of these long-range signals will comprise an address corresponding to each addressable transponder sought to be contacted. Each addressable transponder, in turn, will preferably operate in a scan mode to detect base station signals arriving on any transponder antenna azimuth.
If one or more addressable transponders receive the base station""s long-range signal, each receiving transponder will transmit an acknowledgement (including its address and the transponder antenna azimuth on which the signal was received) back to the base station. By noting the minimum effective range and base station antenna azimuth used to contact a particular transponder, the base station operator can estimate the location (i.e., the azimuth and range) of the transponder. Successive base station transmissions to that transponder at incrementally reduced or increased effective ranges will allow refinement of the range estimate (for example, by incrementally reducing effective range until the transponder is just out of range so that the transponder just fails to acknowledge a base station transmission).
Thus, security information comprising parameters such as effective ranges, antenna azimuths and/or transponder addresses is used frequently in the present invention. But these parameters may be augmented to include, for example, the speed of a vehicle-mounted transponder estimated by use of the vehicle""s speedometer. And another useful parameter that is readily obtained is the closing velocity of a vehicle-mounted transponder with a base station. This closing velocity may be estimated based on Doppler shift in transmissions from the transponder to the base station or vice versa.
Closing velocity may also be estimated by alternative means, including calculation of the component of vehicle speed directed toward or away from a base station through use of the vehicle""s speedometer and its transponder antenna azimuth (reflecting the angle between the direction of forward vehicle speed and the line of communication with the base station) as described herein. In the special case where both the base station and the vehicle are mobile, the closing velocity of a vehicle with a base station would reflect the algebraic sum of the component of vehicle speed toward or away from the base station and the component of base station speed toward or away from the vehicle.
Still more security information related to vehicle operation may be obtained from sensors (e.g., a turning sensor for producing a turning signal indicative of turn-blinker activation in a vehicle, or a hot-wire sensor for producing a hot-wire signal indicative of whether a vehicle has been hot-wired or otherwise improperly started) in a vehicle such as those found in existing OEM and after-market vehicle alarm systems. Such security information may be displayed to vehicle occupants or it may be transmitted to one or more base stations as part of a silent alarm.
Further, a plurality of base stations may be linked in a network covering a geographic area, the extent of which is a function of spacing between base stations and the effective transmission ranges of base stations in the network. One or more operators may interface with such a base station network, preferably at a central location. Note that a base station antenna may be spaced apart from its corresponding receiver and/or transmitter, being connected via one or more links known to those skilled in the art such as micro wave relays, fiber-optic cable, coaxial cable, etc.